Conventionally, various gas generating agents for airbags have been used in inflators for an air bag as a passenger-protecting device in an automobile. As the gas generating agent for airbags, compositions comprising sodium azide have often been used. However, the toxicity of sodium azide to the human body [LD50 (oral−rat)=27 mg/kg] and the hazard thereof at the time of handling are regarded as problematic, and therefore, instead of the above, various gas generating compositions containing nitrogen-containing organic compounds have been developed as safer non-azide gas generating compositions.
U.S. Pat. No. 4,909,549 discloses a composition comprising a hydrogen-containing tetrazole or triazole compound and an oxygen-containing oxidizing agent. U.S. Pat. No. 4,370,181 discloses a gas generating composition comprising a hydrogen-free bitetrazole metal salt and an oxygen-free oxidizing agent. U.S. Pat. No. 4,369,079 discloses a gas generating composition comprising a hydrogen-free bitetrazole metal salt and, an alkali metal nitrate, an alkali metal nitrite, an alkaline earth metal nitrate, an alkaline earth metal nitrite or a mixture thereof. U.S. Pat. No. 5,542,999 discloses a gas generating composition comprising a fuel such as GZT, TAGN, NG (nitroguanidine) or NTO, basic copper nitrate, a catalyst reducing a toxic gas, and a coolant. JP-A 10-72273 discloses a gas generating composition comprising a bitetrazole metal salt, a bitetrazole ammonium salt, or aminotetrazole, and ammonium nitrate.
The structure of the inflator for an air bag has to be optimized in accordance with the properties of the gas generating agent to be used, or the like. WO-A 00/50273 discloses an inflator which uses a non-azide gas generating composition forming less solid residues, specifically, a gas generating composition comprising 54 to 67% of guanidine nitrate and 33 to 46% of an oxidizing agent comprising ammonium perchlorate and sodium nitrate, and does not including a filter. U.S. Pat. No. 6,143,102 discloses in Table 2 that slag can be recovered as solids by adding alumina and silica. In addition, JP-A 11-503104, U.S. Pat. No. 6,126,197, etc. are known.
However, the non-azide, gas generating compositions described above are problematic in the combustion flame temperature, burning rate, phase transition, a generated amount of carbon monoxide and nitrogen oxides, and gas output. When the gas generating composition in U.S. Pat. No. 4,369,079 is actually used, a large amount of a coolant is necessary because of its high combustion flame temperature. The composition in U.S. Pat. No. 5,542,999 may not be completely combustible in a short time because of its low burning rate. In the gas generating agent in JP-A 10-72273, its molded article may be broken by a change in the shape due to the phase transition of ammonium nitrate in the temperature range used, thus failing to achieve stable combustion. In the prior art relating to the non-azide gas generating agent described above, a fuel such as tetrazoles, nitroguanine or TAGN is used, but all of these compounds belong to dangerous substances and require sufficient attention at the time of handling.
WO-A 00/50273 discloses an inflator without a filter by reducing an amount of solids (combustion residues) (disclosed to be reduced to preferably 15% or less) formed upon combustion of the gas generating composition. If combustion residues are released into an airbag, an accident such as damage to the airbag may occur, but in this prior art, the majority of the gas generating composition is converted into a gas by combustion, thus reducing the necessity for separation of combustion residues from the combustion gas by a filter. It is estimated that a generated amount of such combustion residues is influenced by an amount or type of the metal component contained in the gas generating composition. A member corresponding to a filter is not shown in drawings in JP-A 11-503104 and U.S. Pat. No. 6,126,197 wherein like WO-A 00/50273, the amount of the metal component contained in the gas generating agent used is low, thus reducing a generated amount of combustion residues and making a filter unnecessary. When succeeding in making a filter unnecessary, the demand for miniaturization and weight reduction of the inflator can be fulfilled.
U.S. Pat. No. 6,143,102 discloses that slag is recovered as solids by adding alumina and silica, but does not disclose that a filter can be eliminated.